Conventionally, sealed batteries in which a temperature protection device is embedded in resin to prevent abnormal temperature increase are known. In such a sealed battery, as disclosed in JP2002-373631A, for example, a circuit part for controlling charge/discharge and a temperature protection device for preventing excess current or thermal runaway, known as a positive temperature coefficient (PTC) device, are located outside the battery case (housing). JP2002-373631A also discloses an arrangement in which resin covers the circuit part and temperature protection device as well as part of the outer surface of the battery case to improve waterproof properties of the battery.
Generally, a temperature protection device is configured to change its physicality to have a larger resistance as the temperature increases in order to minimize current flowing through it. Accordingly, a temperature protection device has a predetermined maximum rated temperature. When the temperature of the temperature protection device exceeds the maximum rated temperature, the physicality of the temperature protection device changes to lose initial properties of the temperature protection device. Thus, if the temperature protection device comes in direct contact with resin melted during heating, properties of the temperature protection device change, such that expected properties may fail.
To solve this problem, JP2002-373631A discloses an arrangement in which the temperature protection device is covered with a sheet of heat-resistant rubber before the temperature protection device and the heat-resistant rubber are sealed in the resin. Thus, heat of the melted resin is not transmitted directly to the temperature protection device, thereby preventing properties originally possessed by the temperature protection device from being lost due to heat from the resin.
JP2009-135033A discloses an arrangement in which a holder forming a resin invasion prevention chamber is attached to the outside of the battery case such that the temperature protection device does not come in direct contact with melted resin.